EWSR1 and Ewing sarcoma: CIC-DUX4 fusions have been demonstrated in up to two thirds of EWSR1 rearrangement-negative undifferentiated round cell sarcomas of pediatric and young adult patients (Graham et al, 2012; Italiano et al, 2012; Antonescu, 2014), with expression profiling demonstrating a distinct gene signature and suggesting a distinct pathogenesis from Ewing sarcoma (Specht et al, 2014).